Microsoft Security Bulletin MS00-024 - Critical

Summary

Microsoft has released a tool that installs tighter permissions on a Windows NT® 4.0 registry key. The default permissions could allow a malicious user who can interactively log onto a Windows NT 4.0 machine to compromise the cryptographic keys of other users who subsequently log onto the same machine.

General Information

This vulnerability involves a registry key used by the CryptoAPI Base CSPs to specify the driver DLL for a hardware accelerator. By design, such a DLL would have access to users' public and private keys. Although only administrators should have permission to add such a DLL, the permissions on the key actually would allow any user who could interactively log onto the machine to do so. By writing a bogus DLL and installing it, a malicious user could compromise the keys of other users who subsequently used the machine.

The machines primarily at risk would be workstations and terminal servers. If normal security recommendations are followed, normal users will not be allowed to interactively log onto domain controllers, web servers, database servers, ERP servers, and other security-critical machines. Windows NT auditing could be used to determine who changed the key's value. A tool is available that resets the permissions on the affected key to the correct default values. In addition, it incorporates the functionality of the tool provided in Microsoft Security Bulletin MS00-008.

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